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When actress Stephanie March met celebrity chef and Food Network star Bobby Flay more than 10 years ago, he was routinely spending weekends at his house in Southampton on Long Island. "There was an enormous white leather sofa in the living room and four flat-screen TVs," recalls the Texas-born actress, who grew up in a gracious home memorable for its butler's pantry, cedar-lined closets, and a living room appointed for leisurely visiting. "His place smelled like golf," she says.

But it wasn't just Flay's far-from-perfect aesthetics that turned off the elegant March, whose most familiar role as the unsmiling assistant district attorney Alexandra Cabot on Law & Order: Special Victims Unit belies her geniality. A passionate world traveler, she found regular visits to the East End confining. "Why are we here when there's a whole world out there?" she says she often wondered. "And I didn't know a soul," she adds.

It wasn't until the couple attended a friend's wedding in East Hampton years later that March had a change of heart. "We stayed in a cheap hotel and had a blast with a great group of people," she says. But there was still the matter of Flay's beloved bachelor pad, which, it turns out, he didn't love as much as he did Ms. March. "I had to make a choice, so I picked Stephanie," he says. The house, it was decided, would have to go.

Outdoor Dining AreaMarch wasted little time ridding their lives of Flay's unpalatable possessions. She put an ad in the East Hampton Star and staged what turned out to be one of the island's most storied tag sales. "She sold all of my furniture for lunch money!" Flay says with a laugh. Indeed, March prides herself on the sales technique she used that day. "If a customer wanted a chair, I insisted that a set of plates went with it," she says.In the two years following the sale of the home, the couple found three houses they loved, but were outbid on all of them. Others appealed but would require major overhauls. "We had renovated our apartment in the city, and it was tough even though we had the best possible scenario: My business partner was the general contractor, and the guys who built my restaurants did the renovation," says Flay, referring to his six high-end restaurants and 15 burger bars. When the couple learned that a single builder was behind the trio of houses they liked, they surprised themselves by giving him a call.

Screened PorchMarch's wanderlust has never waned—she's an Italophile and regular contributor to the travel website fathomaway.com—but she is rarely happier than when she and Flay flee the city to their custom-built shingle-style home (a Gold LEED–certified one to boot) in the woods of Amagansett, a quiet East Hampton hamlet.

KitchenBy starting from scratch, Flay and March got exactly what they wanted. Flay presided over the designs of his dream indoor and outdoor kitchens but left the rest to his wife. "I've spent my life working a grill, and I never had one at home until now," says Flay. "It took 30 years." Make that a commercial 10-burner stove, two ovens, a fryer, a griddle, and a salamander, along with seating that includes two café tables and a farm table. "I love that my kitchen is technically a restaurant," says Flay, who broke it to city friends last year that he would no longer host his annual Thanksgiving dinner in the couple's Manhattan apartment. "We had 50 people show up for turkey in Amagansett this past holiday anyway. They followed us out here! I prepared two 30-pound turkeys and cooked sides for days. I stand at my kitchen island from the minute I get out here to the minute I leave."

Master BedroomWhich is just the way March imagined it would be. "I was very careful about the floor plan," she says. "I didn't want one that involved a living room cut off from the rest of the house—the kind that you put the Christmas tree in and use only once a year." Instead, March insisted on open spaces, plenty of guest bedrooms and baths, lots of outdoor fabrics covering indoor furnishings, and floors and carpets that could stand up to wet bathing suits, sand, and red wine. And because you can't take the Texas out of the girl, she designed the screened porch as if it were a living room, so that she and her friends could hang out there. "I spend almost all of my time in it—or in the pool, which is long enough for me to do laps," she adds.

Master BathThere was only one major design debate, but it lasted just a day. When Flay lobbied hard to hang a flat-screen television over the fireplace in the living room, March turned to interior designer Tom Delavan—who helped her incorporate the textiles, furnishings, and lighting she has collected from her far-flung travels—to cast the deciding vote. On his urging, she ultimately conceded."He reminded me that everyone likes to watch TV," says the actress. There's that, and perhaps some truth to the idiom that old habits die hard.